This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Vernonia illinoensis, Gleason Native. Perennial. Propagates by seeds. Time of bloom: July to September. Seed-time: September to November. Range: Ontario to Minnesota, southward to Ohio, Illinois, and Iowa. Habitat: Dry prairies; meadows and pastures, roadsides, and waste places.
Stem three to six or more feet tall, rather stout, somewhat rough. Leaves large, oblong lance-shaped, finely woolly-hairy above and rough to the touch beneath, sharply toothed. Heads in a densely crowded cymose cluster, many of them sessile or on very short pedicels, rather large, each containing about forty reddish purple florets; involucre bell-shaped, its bracts purple-tinged, obtuse, closely appressed. Achenes slightly rough-ribbed, the pappus purplish brown. Both pollen and nectar are plentifully supplied by all the Ironweeds, and bumblebees and many species of butterflies are attracted by the flowers, thus assuring their thorough cross-fertilization.
Means of control the same as for Tall Iron weed.